Ion implantation method and apparatus

ABSTRACT

Using a beam current of an ion beam, and a dose amount to a substrate, and an initial value of a scan number of the substrate set to 1, a scan speed of the substrate is calculated. If the scan speed is within the range, the current scan number and the current scan speed are set as a practical scan number and a practical scan speed, respectively. If the scan speed is higher than the upper limit of the range, the calculation process is aborted. If the scan speed is lower than the lower limit of the range, the scan number is incremented by one to calculate a corrected scan number. A corrected scan speed is calculated by using the corrected scan number, etc. The above steps are repeated until the corrected scan speed is within the allowable scan speed range.

TECHNICAL FIELD

The present disclosure relates to an ion implantation method andapparatus for implanting ions into a substrate using both a ribbon-like(this is called also a sheet-like or a strip-like) ion beam in which,with or without performing an X-direction sweep, a dimension in an Xdirection is larger than a dimension in a Y direction that is orthogonalto the X direction, and a mechanical scan of the substrate in adirection intersecting with the principal face of the ion beam. In thespecification, in order to be easily distinguished from a sweep of anion beam, an operation of mechanically sweeping a substrate is referredto as a scan.

RELATED ART

FIG. 9 shows a related-art example of an ion implantation apparatus ofthis kind. The ion implantation apparatus has a configuration whichimplants ions into (for example, a whole face of) a substrate (forexample, a semiconductor substrate) 2 using both a ribbon-like ion beam4 and an operation of mechanically scanning the substrate 2 in adirection intersecting with the principal face 4 b (see FIG. 11) of theion beam 4, by a substrate driving device 10.

Referring to FIG. 11, for example, the ion beam 4 undergoes a sweepprocess in the X direction (for example, a horizontal direction) whichis based on an electric or magnetic field produced by a beam sweeper(not shown), and has a ribbon-like section shape in which the dimensionin the X direction is larger than that in the Y direction (for example,a vertical direction) that is orthogonal to the X direction. Forexample, the ion beam 4 before the sweep operation has a section shapesuch as a small oval or circle as indicated by the reference numeral 4 ain FIG. 11. Alternatively, without undergoing such sweep a process inthe X direction, the ion beam 4 (for example, the ion beam itselfderived from an ion source) may have a ribbon-like section shape inwhich the dimension in the X direction is larger than that in the Ydirection.

In this example, the substrate driving device 10 has: a holder 12 whichholds the substrate 2; a motor 14 which rotates the holder 12 togetherwith the substrate 2 about a center portion 2 a of the substrate 2 asindicated by the arrow A (or in the opposite direction) (this motor isreferred to as the twist motor in order to be distinguished from a motor16 which will be described later); and the motor 16 which drives(reciprocally swings) the holder 12 together with the substrate 2 andthe twist motor 14 as indicated by the arrow B to change the inclinationangle θ of the holder 12 and the substrate 2 (this motor is referred toas the tilt motor in order to be distinguished from the twist motor 14).For example, the inclination angle θ can be changed in a range from 0deg. (i.e., the state where the holder 12 is vertical) to the verticalto 90 deg. (i.e., the state where the holder 12 is horizontal).

The substrate driving device 10 further has a scanning device 18 whichmechanically scans the holder 12, the substrate 2, and the like so as toreciprocate between one end (for example, the lower end) 20 of the scanand the other end (for example, the upper end) 22 as indicated by thearrow C, thereby mechanically scanning the substrate 2 in a direction(for example, the Y direction) intersecting with the principal face 4 bof the ion beam 4. The scan direction of the substrate 2 is notrestricted to the direction of the arrow C (the Y direction). In somecases, the scan may be performed in parallel with the surface of thesubstrate 2. In the specification, one scan of the substrate 2 means aone-way scan.

A substrate driving device having a configuration which is substantiallyidentical with that of the substrate driving device 10 is disclosed inPatent Reference 1.

As shown in FIG. 10, for example, replacement of the substrate 2 withrespect to the holder 12 (for example, that of an ion-implantedsubstrate 2 with a substrate 2 before the ion implantation) is performedwhile the holder 12 is set to a substantially horizontal state at theone end 20 of the scan.

In the ion implantation into the substrate 2, in accordance withExpression 1 or an expression which is mathematically equivalentthereto, for example, the scan number of the substrate 2 is calculatedby using the beam current of the ion beam 4, the dose amount to thesubstrate 2, and a reference scan speed which is used as a reference forcalculating the scan number of the substrate 2. Usually, the calculatedscan number is a mixed decimal with number of digits after the decimalpoint. Therefore, a scan number in which the digits after the decimalpoint are truncated, or which is an integer is calculated, and thecalculated number is set as a scan number which is practically used. Inthe case where the calculated scan number is 3.472, for example, 3 isset as the scan number which is practically used. In accordance withExpression 2 or an expression which is mathematically equivalentthereto, for example, the scan speed which is practically used iscalculated by the scan number which is practically used. In related-art,the ion implantation is performed on the substrate 2 in accordance withthe scan number and scan speed which are calculated in this manner.

$\begin{matrix}{{{scan}\mspace{14mu}{{number}\mspace{14mu}\lbrack{time}\rbrack}} = \frac{\begin{matrix}\begin{matrix}\begin{matrix}{{dose}\mspace{14mu}{{amount}\mspace{14mu}\left\lbrack {{ions}\text{/}{cm}^{2}} \right\rbrack} \times} \\{{reference}\mspace{14mu}{scan}\mspace{14mu}{{speed}\mspace{14mu}\left\lbrack {{cm}\text{/}\sec} \right\rbrack} \times}\end{matrix} \\{{elementary}\mspace{14mu}{electric}\mspace{14mu}{{charge}\mspace{14mu}\lbrack C\rbrack} \times}\end{matrix} \\{coefficient}\end{matrix}}{{beam}\mspace{14mu}{current}\mspace{14mu} \times {10^{- 6}\left\lbrack {C\text{/}\sec} \right\rbrack}}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack \\{{{scan}\mspace{14mu}{{speed}\mspace{14mu}\left\lbrack {{cm}\text{/}\sec} \right\rbrack}} = \frac{\begin{matrix}{{beam}\mspace{14mu}{current} \times {10^{- 6}\left\lbrack {C\text{/}\sec} \right\rbrack} \times} \\{{scan}\mspace{14mu}{number}}\end{matrix}}{\begin{matrix}{{dose}\mspace{14mu}{{amount}\mspace{14mu}\left\lbrack {{ions}\text{/}{cm}^{2}} \right\rbrack} \times} \\{{elementary}\mspace{14mu}{electric}\mspace{14mu}{{charge}\mspace{14mu}\lbrack C\rbrack} \times} \\{coefficient}\end{matrix}}} & \left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Expressions 1 and 2 described above, the elementary electric chargeis 1.602×10⁻¹⁹ [C], and the coefficient is a coefficient which isspecific to the ion implantation apparatus. This is applicable also toExpression 4 which will be described later.

FIG. 12 shows an example of the scan number and scan speed of thesubstrate 2 in the case where the related-art ion implantation method(apparatus) is employed. FIG. 12 is a graph showing transitions of thescan number and the scan speed in the case where the dose amount isfixed and the beam current is reduced. The reference scan speed was 320mm/sec. In order to make the dose amount constant, the scan number isincreased in accordance with reduction of the beam current. In the casewhere the beam current is largely reduced, the scan number is largelyincreased. Also in the case where the beam current is fixed and the doseamount is increased, a similar tendency is obtained.

[Patent Reference 1] JP-A-2004-95434 (Paragraphs [0010] to [0017], FIG.6)

In the vicinities of the ends of the scan of the substrate 2, thesubstrate must be decelerated and accelerated in order to perform thescan return operation, and a time loss is caused by the deceleration andthe acceleration. This will be described in detail with reference toFIG. 13. This time loss is a total of wasted times other than the timeof implantation into the substrate 2 (this time occurs twice per scan)during the time for one scan. Most of the time loss consists of thedeceleration time before the scan return and the acceleration time afterthe scan return. The time loss is the sum of these deceleration andacceleration times and an overscan time (this time also occurs twice perscan) for the overscan of the substrate 2 (the operation in which thesubstrate 2 is overscanned in slightly excess so that the substrate 2 issurely located outside the ion beam 4). For example, the time loss isabout 0.4 sec. per scan in the case where the reference scan speed is320 mm/sec., and about 0.5 sec. per scan in the case where the referencescan speed is 200 mm/sec.

In the specification, the term “scan speed” means the scan speed in theimplantation time and the overscan time.

When the scan number is increased, also the number of decelerations andaccelerations of the substrate in the vicinities of the scan ends isincreased, with the result that many time losses are accumulated, andthe throughput is reduced.

SUMMARY

Exemplary embodiments of the present invention provide an ionimplantation method and apparatus in which accumulation of time losseswhich mainly consist of deceleration and acceleration times in thevicinities of scan ends is suppressed, so that the throughput isimproved.

An ion implantation method according to a first aspect of the inventionis characterized in that the method includes: a scan speed calculatingstep of setting an initial value of a scan number of the substrate to 1,and calculating a scan speed of the substrate by using a beam current ofthe ion beam, a dose amount to the substrate and the initial value of ascan number of the substrate;

a scan speed determining step of: determining whether the scan speed ofthe substrate is within a predetermined allowable scan speed range ornot; if the scan speed is within the allowable scan speed range, settingthe current scan number and the current scan speed as a practical scannumber and a practical scan speed, respectively; if the scan speed ishigher than an upper limit of the allowable scan speed range, aborting aprocess of obtaining the practical scan number and the practical scanspeed; and, if the scan speed is lower than a lower limit of theallowable scan speed range, incrementing the scan number by one tocalculate a corrected scan number;

a corrected-scan speed calculating step of, when the corrected scannumber is calculated, calculating a corrected scan speed by using thecorrected scan number, the beam current, and the dose amount;

a repeating step of, when the corrected scan speed is calculated,performing a process of the scan speed determining step on the correctedscan speed, and repeating the scan speed determining step and thecorrected-scan speed calculating step until the corrected scan speed iswithin the allowable scan speed range; and

an ion implanting step of implanting ions into the substrate inaccordance with the practical scan number and the practical scan speed.

An ion implantation apparatus according to a second aspect of theinvention is characterized in that the apparatus comprises a controllingdevice having a function of performing: (a) a scan speed calculatingprocess of setting an initial value of a scan number of the substrate to1, and calculating a scan speed of the substrate by using a beam currentof the ion beam, and a dose amount to the substrate, and the initialvalue of a scan number of the substrate; (b) a scan speed determiningprocess of: determining whether the scan speed of the substrate iswithin a predetermined allowable scan speed range or not; if the scanspeed is within the allowable scan speed range, setting the current scannumber and the current scan speed as a practical scan number and apractical scan speed, respectively; if the scan speed is higher than anupper limit of the allowable scan speed range, aborting a process ofobtaining the practical scan number and the practical scan speed; and,if the scan speed is lower than a lower limit of the allowable scanspeed range, incrementing the scan number by one to calculate acorrected scan number; (c) a corrected-scan speed calculating processof, when the corrected scan number is calculated, calculating acorrected scan speed by using the corrected scan number, the beamcurrent, and the dose amount; (d) a repeating process of, when thecorrected scan speed is calculated, performing a process of the scanspeed determining step on the corrected scan speed, and repeating thescan speed determining step and the corrected-scan speed calculatingstep until the corrected scan speed is within the allowable scan speedrange; and (e) an ion implanting process of implanting ions into thesubstrate in accordance with the practical scan number and the practicalscan speed.

In the ion implantation method or apparatus, under conditions that thescan speed of the substrate is within the predetermined allowable scanspeed range, ion implantation can be performed in a scan number which isas small as possible. Therefore, accumulation of time losses whichmainly consist of deceleration and acceleration times of the substratein the vicinities of scan ends can be suppressed.

In an ion implantation method and apparatus according to a third aspectof the invention, the scan speed determining step may include a scannumber determining step of, if the scan speed is within the allowablescan speed range, determining whether the current scan number is even orodd; if the current scan number is even, setting the current scan numberand the current scan speed as the practical scan number and thepractical scan speed, respectively; and, if the current scan number isodd, incrementing the scan number by one to calculate a corrected scannumber, and the repeating step may repeat the scan speed determiningstep and the corrected-scan speed calculating step until the correctedscan speed is within the allowable scan speed range and the correctedscan number becomes even.

In an ion implantation method and apparatus according to a fourth aspectof the invention, the function of performing (b) the scan speeddetermining process may include a scan number determining process of, ifthe scan speed is within the allowable scan speed range, determiningwhether the current scan number is even or odd; if the current scannumber is even, setting the current scan number and the current scanspeed as the practical scan number and the practical scan speed,respectively; and, if the current scan number is odd, incrementing thescan number by one to calculate a corrected scan number, and thefunction of performing (d) the repeating process may repeat the scanspeed determining step and the corrected-scan speed calculating stepuntil the corrected scan speed is within the allowable scan speed rangeand the corrected scan number becomes even.

In an ion implantation method and apparatus according to fifth and sixthaspects of the invention, in the scan speed calculating step or the scanspeed calculating process, the initial value of the scan number of thesubstrate may be set to 2 in place of 1.

In an ion implantation method and apparatus according to seventh andeighth aspects of the invention, in the scan speed calculating step orthe scan speed calculating process, the initial value of the scan numberof the substrate may be set to 2 in place of 1, and, in the scan speeddetermining step or the scan speed determining process, the scan numbermay be incremented by 2 in place of one to calculate the corrected scannumber.

An ion implantation method according to a ninth aspect of the inventionis a method of implanting ions into a substrate using both a ribbon-likeion beam in which, with or without performing an X direction sweep, adimension in an X direction is larger than a dimension in a Y directionthat is orthogonal to the X direction, a mechanical scan of thesubstrate in a direction intersecting with a principal face of the ionbeam, and performance of ion implantation while, during a period whenthe ion beam does not impinge on the substrate, rotating the substrateby a step of 360/m deg. about a center portion of the substrate, anddividing one rotation of the substrate into a plurality m of implantingsteps, the method comprising:

a scan speed calculating step of setting an initial value of a scannumber of the substrate per implanting step to 1, and calculating a scanspeed of the substrate by using a beam current of the ion beam, a doseamount to the substrate, a implanting step number, and the initial valueof the scan number of the substrate, and;

a scan speed determining step of: determining whether the scan speed ofthe substrate is within a predetermined allowable scan speed range ornot; if the scan speed is within the allowable scan speed range, settingthe current scan number per implanting step, and the current scan speedas a practical scan number per implanting step, and a practical scanspeed, respectively; if the scan speed is higher than an upper limit ofthe allowable scan speed range, aborting a process of obtaining thepractical scan number per implanting step, and the practical scan speed;and, if the scan speed is lower than a lower limit of the allowable scanspeed range, incrementing the scan number per implanting step by one tocalculate a corrected scan number per implanting step;

a corrected-scan speed calculating step of, when the corrected scannumber per implanting step is calculated, calculating a corrected scanspeed, by using the corrected scan number per implanting step, the beamcurrent, the dose amount, and the implanting step number;

a repeating step of, when the corrected scan speed is calculated,performing a process of the scan speed determining step on the correctedscan speed, and repeating the scan speed determining step and thecorrected-scan speed calculating step until the corrected scan speed iswithin the allowable scan speed range; and

an ion implanting step of implanting ions into the substrate inaccordance with the practical scan number per implanting step and thepractical scan speed.

An ion implantation apparatus according to a tenth aspect of theinvention is an apparatus for implanting ions into a substrate usingboth a ribbon-like ion beam in which, with or without performing an Xdirection sweep, a dimension in an X direction is larger than adimension in a Y direction that is orthogonal to the X direction, amechanical scan of the substrate in a direction intersecting with aprincipal face of the ion beam, and performance of ion implantationwhile, during a period when the ion beam does not impinge on thesubstrate, rotating the substrate by a step of 360/m deg. about a centerportion of the substrate, and dividing one rotation of the substrateinto a plurality m of implanting steps, the apparatus comprising:

a controlling device having a function of performing: (a) a scan speedcalculating process of setting an initial value of a scan number of thesubstrate per implanting step to 1, and calculating a scan speed of thesubstrate by using a beam current of the ion beam, a dose amount to thesubstrate, a implanting step number and the initial value of the scannumber of the substrate per implanting step; (b) a scan speeddetermining process of: determining whether the scan speed of thesubstrate is within a predetermined allowable scan speed range or not;if the scan speed is within the allowable scan speed range, setting thecurrent scan number per implanting step, and the current scan speed as apractical scan number per implanting step, and a practical scan speed,respectively; if the scan speed is higher than an upper limit of theallowable scan speed range, aborting a process of obtaining thepractical scan number per implanting step, and the practical scan speed;and, if the scan speed is lower than a lower limit of the allowable scanspeed range, incrementing the scan number per implanting step by one tocalculate a corrected scan number per implanting step; (c) acorrected-scan speed calculating process of, when the corrected scannumber per implanting step is calculated, calculating a corrected scanspeed, by using the corrected scan number per implanting step, the beamcurrent, the dose amount, and the implanting step number; (d) arepeating process of, when the corrected scan speed is calculated,performing a process of the scan speed determining step on the correctedscan speed, and repeating the scan speed determining step and thecorrected-scan speed calculating step until the corrected scan speed iswithin the allowable scan speed range; and (e) an ion implanting processof implanting ions into the substrate in accordance with the practicalscan number per implanting step and the practical scan speed.

In the ion implantation method or apparatus, under conditions that thescan speed of the substrate is within the predetermined allowable scanspeed range, ion implantation can be performed in a scan number perimplanting step which is as small as possible. Therefore, accumulationof time losses which mainly consist of deceleration and accelerationtimes of the substrate in the vicinities of scan ends can be suppressed.

In an ion implantation method and apparatus according to an eleventh andtwelfth aspect of the invention, the implanting step number may beeven-numbered.

According to the inventions set forth in the first, second, fifth andsixth aspects, under conditions that the scan speed of the substrate iswithin the predetermined allowable scan speed range, ion implantationcan be performed in a scan number which is as small as possible.Therefore, accumulation of time losses which mainly consist ofdeceleration and acceleration times in the vicinities of scan ends canbe suppressed, and the throughput can be improved.

According to the inventions set forth in the third, fourth, seventh andeighth aspects, under conditions that the scan speed of the substrate iswithin the predetermined allowable scan speed range, ion implantationcan be performed in a scan number which is as small as possible.Therefore, accumulation of time losses which mainly consist ofdeceleration and acceleration times of the substrate in the vicinitiesof scan ends can be suppressed, and the throughput can be improved.

Moreover, the practical scan number of the substrate can be surelyeven-numbered. As a result, a time loss due to the moving time for oneextra scan in the case where the scan number is odd can be eliminated.Also from this viewpoint, therefore, the throughput can be improved.

According to the inventions set forth in the ninth and tenth aspects,under conditions that the scan speed of the substrate is within thepredetermined allowable scan speed range, ion implantation can beperformed in a scan number per implanting step which is as small aspossible. Therefore, accumulation of time losses which mainly consist ofdeceleration and acceleration times of the substrate in the vicinitiesof scan ends can be suppressed, and the throughput can be improved.

According to the inventions set forth in the eleventh and twelfthaspects, the implanting step number is even, and hence the total scannumber can be surely even-numbered irrespective of whether the scannumber per implanting step is odd or even. As a result, a time loss dueto the moving time of one extra scan in the case where the total scannumber is odd can be eliminated. Also from this viewpoint, therefore,the throughput can be improved.

Other features and advantages may be apparent from the followingdetailed description, the accompanying drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing an embodiment of an ion implantationapparatus for implementing the ion implantation method of the invention.

FIG. 2 is a flowchart showing an embodiment of the ion implantationmethod of the invention.

FIG. 3 is a flowchart showing another embodiment of the ion implantationmethod of the invention.

FIG. 4 is a flowchart showing a further embodiment of the ionimplantation method of the invention.

FIG. 5 is a flowchart showing a still further embodiment of the ionimplantation method of the invention.

FIG. 6 is a view showing an example of a scan number and scan speed of asubstrate in the case where the ion implantation method of the inventionis employed.

FIG. 7 is a diagram showing an example of step implantation.

FIG. 8 is a flowchart showing a still further embodiment of the ionimplantation method of the invention.

FIG. 9 is a side view showing an example of an ion implantationapparatus for implementing a related-art ion implantation method.

FIG. 10 is a view showing an example of a state of a substrate drivingdevice in replacement of a substrate.

FIG. 11 is a perspective view partly showing an example of a ribbon-likeion beam.

FIG. 12 is a view showing an example of the scan number and scan speedof the substrate in the case where the related-art ion implantationmethod is employed.

FIG. 13 is a view showing an example of a transition of a speed in onescan of the substrate.

DETAILED DESCRIPTION

FIG. 1 is a side view showing an embodiment of an ion implantationapparatus for implementing the ion implantation method of the invention.The portions which are identical or corresponding to those of therelated-art example shown in FIGS. 9 to 11 are denoted by the samereference numerals, and, in the following description, emphasis isplaced on differences from the related-art example.

The ion implantation apparatus includes, in addition to theconfiguration of the above-described related-art ion implantationapparatus, a controlling device 30 having a function of performing acalculation control which will be described later, and a beam currentmeasuring device 32 which measures the beam current of the ion beam 4.

The beam current of the ion beam 4, and the dose amount of the substrate2 are given to the controlling device 30. In the embodiment, morespecifically, a measurement value which is measured by the beam currentmeasuring device 32 is given as the beam current of the ion beam 4. Thedose amount is given as a preset value.

The beam current measuring device 32 is, for example, a Faraday cup, andreceives the ion beam 4 which is conducting the ion implantation intothe substrate 2, at a position where the device does not interfere withthe ion implantation into the substrate 2 (for example, in the vicinityof one end in the X direction of the ribbon-like ion beam 4), andmeasures the beam current of the ion beam.

The controlling device 30 has a function of controlling the substratedriving device 10, specifically, the scanning device 18, twist motor 14,and tilt motor 16 which constitute the substrate driving device. Morespecifically, the controlling device 30 performs the calculation controlwhich will be described below, to implement an ion implantation methodwhich will be described below. An example will be described withreference to FIG. 2.

As described above, the beam current of the ion beam 4, and the doseamount of the substrate 2 are given to the controlling device 30 (step100). Furthermore, 1 is given as an initial value of the scan number(for example, 1 is set, step 101). In accordance with Expression 2described above or an expression which is mathematically equivalentthereto, for example, the speed of the scan of the substrate 2 which isperformed for realizing the dose amount by the substrate driving device10 (more specifically, the scanning device 18) is calculated by usingthese values (step 102). The steps 100 to 102 constitute a scan speedcalculating step.

Next, it is determined whether the scan speed of the substrate 2, morespecifically, the above-calculated scan speed or a corrected scan speedwhich will be described later is within a predetermined allowable scanspeed range or not (step 103). For example, the allowable scan speedrange is a speed range which can be realized by the scanning device 18,such as a range from 100 mm/sec. to 320 mm/sec.

If the scan speed is within the allowable scan speed range, the currentscan number and the current scan speed are set as a practical scannumber (namely, which is to be practically used, the same shall applyhereinafter) and a practical scan speed, respectively (step 104). If thescan speed is higher than the upper limit of the allowable scan speedrange, the process of obtaining the practical scan number and thepractical scan speed is aborted (step 105), because, even when the scannumber is later increased, only a situation where the scan speed isincreased is produced, and therefore the scan speed cannot be caused tobe within the allowable scan speed range. In this case, for example, theimplantation conditions (the beam current and the dose amount) arechanged, and the process is are again performed with starting from step100. If the scan speed is lower than the lower limit of the allowablescan speed range, the scan number is incremented by 1 to calculate thecorrected scan number (step 106). The steps 103 to 106 constitute a scanspeed determining step.

In the case where the corrected scan number is calculated, in accordancewith Expression 2 described above or an expression which ismathematically equivalent thereto, for example, the corrected scan speedof the substrate 2 for realizing the dose amount is calculated by usingthe corrected scan number, the beam current, and the dose amount (step107). This step is a corrected-scan speed calculating step.

In the case where the corrected scan speed is calculated, then, theprocess returns to step 103, and the scan speed determining step isperformed on the corrected scan speed to repeat the scan speeddetermining step and the corrected-scan speed calculating step until thecorrected scan speed is within the allowable scan speed range. This stepis a repeating step. Therefore, the scan number is incremented by a stepof 1 from the initial value of 1.

As a result, the practical scan number and the practical scan speed areobtained (step 104), and hence ion implantation is performed on thesubstrate 2 in accordance with the practical scan number and thepractical scan speed (step 108). This step is an ion implanting step.

Preferably, the beam current of the ion beam 4 is not a preset value buta value measured by the beam current measuring device 32 as in theembodiment. According to the configuration, even when the beam currentfluctuates during ion implantation into the single substrate 2, acontrol of changing the scan speed in direct proportion to the beamcurrent can be performed, so that uniform ion implantation in the Ydirection can be realized without being affected by the fluctuation ofthe beam current. The control in which the scan speed is in directproportion to the beam current as described above is disclosed also in,for example, JP-A-3-114128 (see the upper left column of page 2) andJapanese Patent No. 3,692,999 (see Paragraph [0037]) .

In the ion implantation in step 108, there are two cases: (a) the ionimplantation into the single substrate 2 is always performed at the scanspeed; and (b) the ion implantation is performed with using also acontrol in which, while using the practical scan speed as a reference,the scan speed is in direct proportion to the beam current as describedabove during ion implantation into the single substrate 2. The term “inaccordance with the practical scan speed” in step 108 described above isused in the meaning that both the cases (a) and (b) are included. Thisis applicable also to ion implantation (steps 108, 118) in otherembodiments which will be described later.

In the embodiment, the controlling device 30 has a function ofperforming: a scan speed calculating process which is identical incontent to the scan speed calculating step; a scan speed determiningprocess which is identical in content to the scan speed determiningstep; a corrected-scan speed calculating process which is identical incontent to the corrected-scan speed calculating step; a repeatingprocess which is identical in content to the repeating step; and an ionimplanting process which is identical in content to the ion implantingstep. The controlling device has a further function of performing acontrol in which the scan speed is in direct proportion to the beamcurrent as described above during ion implantation into the substrate 2.

In the ion implantation method (apparatus) of the embodiment, underconditions that the scan speed of the substrate 2 is within thepredetermined allowable scan speed range, ion implantation can beperformed in a scan number which is as small as possible. Therefore,accumulation of time losses (for example, about 0.4 to 0.5 sec. perscan) which mainly consist of deceleration and acceleration times of thesubstrate 2 in the vicinities of scan ends can be suppressed, and thethroughput can be improved.

When the scan number is reduced, the scan speed is lowered in order torealize the same dose amount (see Expression 2), but the implantationtime of the substrate 2 is not changed. From this point of view, thethroughput is not reduced. This will be described by way of an example.It is assumed that an implantation time which is required for implantinga desired dose amount at a certain beam current is, for example, 6 sec.Even when implantation is performed in six split implantation times of 1sec., or in three split implantation times of 2 sec., the totalimplantation time is 6 sec. or unchanged.

Examples of results of the measurement of the throughput will be brieflydescribed. When the scan number was reduced from nine to three, thethroughput was improved by about 7%, and, when the scan number wasreduced from seven to three, the throughput was improved by about 5%.

Next, another embodiment will be described with reference to FIGS. 3 to5 and 8. The portions which are identical or corresponding to those ofFIG. 2 are denoted by the same reference numerals, and, in the followingdescription, emphasis is placed on differences from FIG. 2.

In the embodiment shown in FIG. 3, step 109 is added to the flowchart ofFIG. 2. If it is determined in step 103 described above that the scanspeed of the substrate 2 is within the predetermined allowable scanspeed range, it is determined whether the scan number is even or odd(step 109). If the scan number is even, the control proceeds to step 104described above, and the scan number and the scan speed are set as thepractical scan number and the practical scan speed, respectively. If thescan number is odd, the control proceeds to step 106 described above,and the scan number is incremented by 1 to calculate the corrected scannumber.

In the embodiment shown in FIG. 3, in place of the above-described scanspeed determining step, there is a scan speed determining step includinga scan number determining step, which is configured by steps 103 to 106and 109 described above.

In the embodiment shown in FIG. 3, the controlling device 30 has afunction of performing a scan speed determining step including a scannumber determining step which is identical in content to the scan speeddetermining step including the scan number determining step, in place ofthe scan speed determining process.

In the ion implantation method (apparatus) of the embodiment shown inFIG. 3, similarly with the embodiment shown in FIG. 2, under conditionsthat the scan speed of the substrate 2 is within the predeterminedallowable scan speed range, ion implantation can be performed in a scannumber which is as small as possible. Therefore, accumulation of timelosses which mainly consist of deceleration and acceleration times ofthe substrate 2 in the vicinities of scan ends can be suppressed, andthe throughput can be improved.

Moreover, the practical scan number of the substrate 2 can be surelyeven-numbered. As a result, a time loss due to the moving time of oneextra scan in the case where the scan number is odd can be eliminated.Also from this viewpoint, the throughput can be improved.

Effects due to the configuration where the practical scan number iseven-numbered will be described in more detail.

In the case where the scan number of the substrate 2 is odd, asindicated by the dash-dot-dot line in FIG. 1, the substrate 2, theholder 12, and the like at the end of the ion implantation into thesubstrate 2 are located in the other end 22 of the scan. As describedabove, the position of replacement of the substrate 2 with respect tothe holder 12 is in the end 20 of the scan (see also FIG. 10). After theion implantation, therefore, the substrate 2, the holder 12, and thelike must be moved (in this example, lowered) by a distancecorresponding to one scan. The moving time for the one scan is extra andbecomes a time loss. For example, the time loss per substrate is about 1to 1.6 sec. The time loss causes the throughput of the ion implantationto be lowered.

By contrast, in the case where the practical scan number is surelyeven-numbered, the time loss due to the moving time for the one scan canbe eliminated, and therefore the throughput can be improved.

Results of measurements of the throughput in the case where both thereduction of the scan number and the even numbering are used as in theembodiment shown in FIG. 3 will be briefly exemplified. When the scannumber was reduced from nine to four, the throughput was improved byabout 10%, and, when the scan number was reduced from seven to four, thethroughput was improved by about 10%.

In an embodiment shown in FIG. 4, the initial value in step 101 in theflowchart of FIG. 2 is set to 2.

Also in the ion implantation method (apparatus) of the embodiment, asdescribed in the embodiment shown in FIG. 2, under conditions that thescan speed of the substrate 2 is within the predetermined allowable scanspeed range, ion implantation can be performed in a scan number which isas small as possible. Therefore, accumulation of time losses whichmainly consist of deceleration and acceleration times of the substrate 2in the vicinities of scan ends can be suppressed, and the throughput canbe improved.

An embodiment shown in FIG. 5 is configured so that, in step 106 of theflowchart of FIG. 4, the corrected scan number is calculated while thescan number is incremented by 2 in place of the increment of one.

Also in the ion implantation method (apparatus) of the embodiment, asdescribed in the embodiment shown in FIG. 4, under conditions that thescan speed of the substrate 2 is within the predetermined allowable scanspeed range, ion implantation can be performed in a scan number which isas small as possible. Therefore, accumulation of time losses whichmainly consist of deceleration and acceleration times of the substrate 2in the vicinities of scan ends can be suppressed, and the throughput canbe improved.

Moreover, the practical scan number can be surely even-numbered. Asdescribed in the embodiment shown in FIG. 3, therefore, a time loss dueto the moving time of one extra scan in the case where the scan numberis odd can be eliminated, and the throughput can be improved.

FIG. 6 shows an example of the practical scan number and practical scanspeed of the substrate 2 in the case where the ion implantation method(apparatus) of the embodiment shown in FIG. 5 is employed. FIG. 6 is agraph which, in a similar manner as FIG. 12, shows transitions of thepractical scan number and the practical scan speed in the case where thedose amount is fixed and the beam current is reduced. The dose amount isequal to that in the case of FIG. 12. The maximum scan speed is equal tothe reference scan speed in the case of FIG. 12. In accordance withreduction of the beam current, the scan number is increased. However, itis seen that the increase is suppressed to a very small degree ascompared with the case of FIG. 12, and the scan number is always even.Also in the case where the beam current is fixed and the dose amount isincreased, a similar tendency is observed, and the scan number isincreased while maintained to be even.

Next, an embodiment in which step implantation is performed will bedescribed. In step implantation, ion implantation is performed while,during a period when the ion beam 4 does not impinge on the substrate 2,the substrate 2 is rotated by a step of 360/m deg. about the centerportion 2 a of the substrate 2 in, for example, the direction of thearrow A (or the opposite direction), and one rotation of the substrateis divided into a plurality (namely, an integer of two or more) m ofimplanting steps. Namely, m is the implanting step number. Theimplantation method is also called step rotation implantation. In theembodiment, the twist motor 14 of the substrate driving device 10 isused for the rotation of the substrate 2.

The scan number n per implanting step is an integer of one or more.Therefore, the total scan number N is expressed by the followingexpression.N=mn[time]  [Expression 3]

FIG. 7 shows an example in the case where the implanting step number mis 2, the scan number n per implanting step is 2, and the total scannumber N is 4. In this case, two scans or scans S₁ and S₂ are performedon the substrate 2 in a first implanting step ((A) of FIG. 7), thesubstrate 2 is then rotated by 180 (=360/2) deg. ((B) of FIG. 7), andtwo scans or scans S₃ and S₄ are then performed on the substrate 2 in asecond implanting step ((C) of FIG. 7). In the embodiment, the scans S₁to S₄ are performed by using the scanning device 18 of the substratedriving device 10. The detail of this is as described above.

FIG. 8 shows a flowchart in the case where the step implantation isperformed. The flowchart will be described while emphasis is placed ondifferences from FIG. 2.

In the embodiment, the beam current of the ion beam 4, the dose amountto the substrate 2, and the implanting step number are given to thecontrolling device 30 (step 110). Furthermore, 1 is given as an initialvalue of the scan number per implanting step (for example, 1 is set,step 111).

In accordance with Expression 4 described below or an expression whichis mathematically equivalent thereto, for example, the speed of the scanof the substrate 2 which is performed for realizing the dose amount bythe substrate driving device 10 (more specifically, the scanning device18) is calculated by using these values (step 112). The steps 110 to 112constitute the scan speed calculating step.

$\begin{matrix}{{{scan}\mspace{14mu}{{speed}\mspace{14mu}\left\lbrack {{cm}\text{/}\sec} \right\rbrack}} = \frac{\begin{matrix}{{implanting}\mspace{14mu}{step}\mspace{14mu}{number} \times} \\{{beam}\mspace{14mu}{current} \times {10^{- 6}\left\lbrack {C\text{/}\sec} \right\rbrack} \times} \\\begin{matrix}{{scan}\mspace{14mu}{number}\mspace{14mu}{per}} \\{{implanting}\mspace{14mu}{{step}\mspace{14mu}\lbrack{time}\rbrack}}\end{matrix}\end{matrix}}{\begin{matrix}{{dose}\mspace{14mu}{{amount}\mspace{14mu}\left\lbrack {{ions}\text{/}{cm}^{2}} \right\rbrack} \times} \\{{elementary}\mspace{14mu}{electric}\mspace{14mu}{{charge}\lbrack C\rbrack} \times} \\{coefficient}\end{matrix}}} & \left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Steps 113, 115 are substantially identical with the steps 103, 105 ofFIG. 2, respectively.

If the scan speed is within the allowable scan speed range, the currentscan number per implanting step and the current scan speed are set as apractical scan number per implanting step and a practical scan speed,respectively (step 114). If the scan speed is lower than the limit ofthe allowable scan speed range, the scan number per implanting step isincremented by 1 to calculate the corrected scan number per implantingstep (step 116). The steps 113 to 116 constitute the scan speeddetermining step.

In the case where the corrected scan number per implanting step iscalculated, in accordance with Expression 4 described above or anexpression which is mathematically equivalent thereto, for example, thecorrected scan speed of the substrate 2 for realizing the dose amount iscalculated by using the corrected scan number per implanting step, thebeam current, and the dose amount (step 117). This step is thecorrected-scan speed calculating step.

In the case where the corrected scan speed is calculated, then, theprocess returns to step 113, and the scan speed determining step isperformed on the corrected scan speed to repeat the scan speeddetermining step and the corrected-scan speed calculating step until thecorrected scan speed is within the allowable scan speed range. This stepis the repeating step. Therefore, the scan number per implanting step isincremented by a step of 1 from the initial value of 1.

As a result, the practical scan number per implanting step and thepractical scan speed are obtained (step 114), and hence ion implantationis performed on the substrate 2 in accordance with the number and thespeed (step 118). This step is the ion implanting step.

In the embodiment, the controlling device 30 has a function ofperforming: a scan speed calculating process which is identical incontent to the scan speed calculating step; a scan speed determiningprocess which is identical in content to the scan speed determiningstep; a corrected-scan speed calculating process which is identical incontent to the corrected-scan speed calculating step; a repeatingprocess which is identical in content to the repeating step; and an ionimplanting process which is identical in content to the ion implantingstep. The controlling device has a further function of performing acontrol in which the scan speed is in direct proportion to the beamcurrent as described above during ion implantation into the substrate 2.

In the ion implantation method (apparatus) of the embodiment, underconditions that the scan speed of the substrate is within thepredetermined allowable scan speed range, ion implantation can beperformed in a scan number per implanting step which is as small aspossible. Therefore, accumulation of time losses which mainly consist ofdeceleration and acceleration times of the substrate 2 in the vicinitiesof scan ends can be suppressed, and the throughput can be improved.

The implanting step number which is given in step 110 may beeven-numbered. According to the configuration, the total scan number canbe surely even-numbered irrespective of whether the scan number perimplanting step is odd or even. As a result, a time loss due to themoving time of the above-described one extra scan in the case where thetotal scan number is odd can be eliminated. Also from this viewpoint,the throughput can be improved. The detail of the scan process is asdescribed above in the embodiment of FIG. 3.

1. An ion implantation method of implanting ions into a substrate usingboth a ribbon-like ion beam in which, with or without performing an Xdirection sweep, a dimension in an X direction is larger than adimension in a Y direction that is orthogonal to the X direction, and amechanical scan of the substrate in a direction intersecting with aprincipal face of the ion beam, said method comprising: a scan speedcalculating step of setting an initial value of a scan number of thesubstrate to 1, and calculating a scan speed of the substrate by using abeam current of the ion beam, a dose amount to the substrate and theinitial value of a scan number of the substrate; a scan speeddetermining step of: determining whether the scan speed of the substrateis within a predetermined allowable scan speed range or not; if the scanspeed is within the allowable scan speed range, setting the current scannumber and the current scan speed as a practical scan number and apractical scan speed, respectively; if the scan speed is higher than anupper limit of the allowable scan speed range, aborting a process ofobtaining the practical scan number and the practical scan speed; and,if the scan speed is lower than a lower limit of the allowable scanspeed range, incrementing the scan number by one to calculate acorrected scan number; a corrected-scan speed calculating step of, whenthe corrected scan number is calculated, calculating a corrected scanspeed by using the corrected scan number, the beam current, and the doseamount; a repeating step of, when the corrected scan speed iscalculated, performing a process of said scan speed determining step onthe corrected scan speed, and repeating said scan speed determining stepand said corrected-scan speed calculating step until the corrected scanspeed is within the allowable scan speed range; and an ion implantingstep of implanting ions into the substrate in accordance with thepractical scan number and the practical scan speed.
 2. An ionimplantation apparatus for implanting ions into a substrate using both aribbon-like ion beam in which, with or without performing an X directionsweep, a dimension in an X direction is larger than a dimension in a Ydirection that is orthogonal to the X direction, and a mechanical scanof the substrate in a direction intersecting with a principal face ofthe ion beam, said apparatus comprising: a controlling device having afunction of performing: (a) a scan speed calculating process of settingan initial value of a scan number of the substrate to 1, and calculatinga scan speed of the substrate by using a beam current of the ion beam,and a dose amount to the substrate, and the initial value of a scannumber of the substrate; (b) a scan speed determining process of:determining whether the scan speed of the substrate is within apredetermined allowable scan speed range or not; if the scan speed iswithin the allowable scan speed range, setting the current scan numberand the current scan speed as a practical scan number and a practicalscan speed, respectively; if the scan speed is higher than an upperlimit of the allowable scan speed range, aborting a process of obtainingthe practical scan number and the practical scan speed; and, if the scanspeed is lower than a lower limit of the allowable scan speed range,incrementing the scan number by one to calculate a corrected scannumber; (c) a corrected-scan speed calculating process of, when thecorrected scan number is calculated, calculating a corrected scan speedby using the corrected scan number, the beam current, and the doseamount; (d) a repeating process of, when the corrected scan speed iscalculated, performing a process of said scan speed determining step onthe corrected scan speed, and repeating said scan speed determining stepand said corrected-scan speed calculating step until the corrected scanspeed is within the allowable scan speed range; and (e) an ionimplanting process of implanting ions into the substrate in accordancewith the practical scan number and the practical scan speed.
 3. An ionimplantation method according to claim 1, wherein the scan speeddetermining step includes a scan number determining step of, if the scanspeed is within the allowable scan speed range, determining whether thecurrent scan number is even or odd; if the current scan number is even,setting the current scan number and the current scan speed as thepractical scan number and the practical scan speed, respectively; and,if the current scan number is odd, incrementing the scan number by oneto calculate a corrected scan number, and wherein the repeating steprepeats said scan speed determining step and said corrected-scan speedcalculating step until the corrected scan speed is within the allowablescan speed range and the corrected scan number becomes even.
 4. An ionimplantation apparatus according to claim 2, wherein the function ofperforming (b) the scan speed determining process includes a scan numberdetermining process of, if the scan speed is within the allowable scanspeed range, determining whether the current scan number is even or odd;if the current scan number is even, setting the current scan number andthe current scan speed as the practical scan number and the practicalscan speed, respectively; and, if the current scan number is odd,incrementing the scan number by one to calculate a corrected scannumber, and wherein the function of performing (d) the repeating processrepeats said scan speed determining step and said corrected-scan speedcalculating step until the corrected scan speed is within the allowablescan speed range and the corrected scan number becomes even.
 5. An ionimplantation method according to claim 1, wherein, in said scan speedcalculating step, the initial value of the scan number of the substrateis set to 2 in place of
 1. 6. An ion implantation apparatus according toclaim 2, wherein, in said scan speed calculating process of saidcontrolling device, the initial value of the scan number of thesubstrate is set to 2 in place of
 1. 7. An ion implantation methodaccording to claim 1, wherein, in said scan speed calculating step, theinitial value of the scan number of the substrate is set to 2 in placeof 1, and, in said scan speed determining step, the scan number isincremented by 2 in place of one to calculate the corrected scan number.8. An ion implantation apparatus according to claim 2, wherein, in saidscan speed calculating process of said controlling device, the initialvalue of the scan number of the substrate is set to 2 in place of 1,and, in said scan speed determining process, the scan number isincremented by 2 in place of one to calculate the corrected scan number.9. An ion implantation method of implanting ions into a substrate usingboth a ribbon-like ion beam in which, with or without performing an Xdirection sweep, a dimension in an X direction is larger than adimension in a Y direction that is orthogonal to the X direction, amechanical scan of the substrate in a direction intersecting with aprincipal face of the ion beam, and performance of ion implantationwhile, during a period when the ion beam does not impinge on thesubstrate, rotating the substrate by a step of 360/m deg. about a centerportion of the substrate, and dividing one rotation of the substrateinto a plurality m of implanting steps, said method comprising: a scanspeed calculating step of setting an initial value of a scan number ofthe substrate per implanting step to 1, and calculating a scan speed ofthe substrate by using a beam current of the ion beam, a dose amount tothe substrate, a implanting step number, and the initial value of thescan number of the substrate, and; a scan speed determining step of:determining whether the scan speed of the substrate is within apredetermined allowable scan speed range or not; if the scan speed iswithin the allowable scan speed range, setting the current scan numberper implanting step, and the current scan speed as a practical scannumber per implanting step, and a practical scan speed, respectively; ifthe scan speed is higher than an upper limit of the allowable scan speedrange, aborting a process of obtaining the practical scan number perimplanting step, and the practical scan speed; and, if the scan speed islower than a lower limit of the allowable scan speed range, incrementingthe scan number per implanting step by one to calculate a corrected scannumber per implanting step; a corrected-scan speed calculating step of,when the corrected scan number per implanting step is calculated,calculating a corrected scan speed by using the corrected scan numberper implanting step, the beam current, the dose amount, and theimplanting step number; a repeating step of, when the corrected scanspeed is calculated, performing a process of said scan speed determiningstep on the corrected scan speed, and repeating said scan speeddetermining step and said corrected-scan speed calculating step untilthe corrected scan speed is within the allowable scan speed range; andan ion implanting step of implanting ions into the substrate inaccordance with the practical scan number per implanting step and thepractical scan speed.
 10. An ion implantation apparatus for implantingions into a substrate using both a ribbon-like ion beam in which, withor without performing an X direction sweep, a dimension in an Xdirection is larger than a dimension in a Y direction that is orthogonalto the X direction, a mechanical scan of the substrate in a directionintersecting with a principal face of the ion beam, and performance ofion implantation while, during a period when the ion beam does notimpinge on the substrate, rotating the substrate by a step of 360/m deg.about a center portion of the substrate, and dividing one rotation ofthe substrate into a plurality m of implanting steps, said apparatuscomprising: a controlling device having a function of performing: (a) ascan speed calculating process of setting an initial value of a scannumber of the substrate per implanting step to 1, and calculating a scanspeed of the substrate by using a beam current of the ion beam, a doseamount to the substrate, a implanting step number and the initial valueof the scan number of the substrate per implanting step; (b) a scanspeed determining process of: determining whether the scan speed of thesubstrate is within a predetermined allowable scan speed range or not;if the scan speed is within the allowable scan speed range, setting thecurrent scan number per implanting step, and the current scan speed as apractical scan number per implanting step, and a practical scan speed,respectively; if the scan speed is higher than an upper limit of theallowable scan speed range, aborting a process of obtaining thepractical scan number per implanting step, and the practical scan speed;and, if the scan speed is lower than a lower limit of the allowable scanspeed range, incrementing the scan number per implanting step by one tocalculate a corrected scan number per implanting step; (c) acorrected-scan speed calculating process of, when the corrected scannumber per implanting step is calculated, calculating a corrected scanspeed, by using the corrected scan number per implanting step, the beamcurrent, the dose amount, and the implanting step number; (d) arepeating process of, when the corrected scan speed is calculated,performing a process of said scan speed determining step on thecorrected scan speed, and repeating said scan speed determining step andsaid corrected-scan speed calculating step until the corrected scanspeed is within the allowable scan speed range; and (e) an ionimplanting process of implanting ions into the substrate in accordancewith the practical scan number per implanting step and the practicalscan speed.
 11. An ion implantation method according to claim 9, whereinthe implanting step number is even.
 12. An ion implantation apparatusaccording to claim 10, wherein the implanting step number is even.